[U-Boot] [RFC PATCH 2/3] sunxi: video: Add video driver for H3 SoC

[Maxime Ripard <maxime.ripard@free-electrons.com>]

Hi,

On Wed, Dec 14, 2016 at 11:11:19PM +0100, Jernej ?krabec wrote:
> > > While I took Rockchip HDMI code for reference, it can't be easily reused.
> > > First of, it uses DT nodes. I guess I could write DT binding or modify
> > > existing driver to work without it.
> > 
> > Like we discussed in the other part of the thread, I think the latter
> > would be easier to deal with.
> 
> I forgot to mention that it also uses driver model. The way I would go with 
> this is to split out common code to dwc_hdmi.c and have platform dependant 
> drivers for Rockchip, Allwinner, etc. Basically the same way as it is done in 
> Linux.

That sounds reasonable.

> > > Thirdly, and in my opinion most annoying, Rockchip driver uses 32
> > > bit aligned registers, but H3 does not. This also means a lot of
> > > work to make it more generic.
> > 
> > How does Linux deal with that? Would just using some kind of accessors
> > that would abstract that away from the driver help, or is it more
> > complicated?
> 
> Yes, Linux driver checks "reg-io-width" property and selects accessors 
> accordingly. I suppose I could do similar, save function pointer in a driver 
> private data. I suppose it is ok that platform specific code initializes this 
> private data?

Something like passing a flag stored in the platform data (and/or read
from DT for the relevant cases) to a generic accessor would also be a
solution, without the need for everyone to implement its accessors.

> > > Actually, H3 is more similar to i.MX6 HDMI in this regard, but
> > > driver's code is scattered throughout multiple files (search for
> > > mxc_hdmi.h inclusion). It is certainly doable, but it will take much
> > > more time.  Basically, U-Boot already has two drivers for DWC HDMI
> > > and with this patch it will get third. Merging all three
> > > implementations into one would be very tedious, but very desirable
> > > goal. I must state that I didn't really try to understand i.MX6 HDMI
> > > code at all, so I don't now how hard it would be to pull it out.
> > 
> > I'm not sure that merging a third and saying that it would be up to
> > the fourth to do the work is reasonable. It's just hiding an issue
> > under the carpet, but I don't see how it will be easier for the next
> > person to work on that. Quite the opposite actually.
> 
> True. I wonder if Renesas already prepared U-Boot DWC HDMI driver...
> 
> Do you think it makes sense to put all files related to Allwinner
> video drivers to sunxi subfolder? There will be at least 4 .c files
> according to my plan and even more in the future (at least for TV
> out driver).

On principle, I don't see anything wrong with that.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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